1. Field of Invention
This invention relates to systems and methods for fabricating internal die filters.
2. Description of Related Art
In a wide range of fluid processing applications, including those in the printing, medical, chemical, biochemical, genetic, automotive and energy fields, it is necessary to separate particles out of the fluid. For example, foreign particles or internally-generated particles may interfere with the subsequent intended use of the fluid, by potentially obstructing a small fluidic passageway in a critical region. Alternatively, the particles generated in the process may be a desired product. Consequently, it is necessary or desirable to capture such particles.
In particular, there is a class of devices, called microfluidic devices, in which a fluid enters the device and is then processed in some way by the device. Such microfluidic devices typically have an inlet for the fluid, a fluid processing region, and small fluidic passageways which bring the fluid from the inlet to the fluid processing region, and optionally, from the processing region to an outlet.
In some applications, a filter is fabricated which is internal to the microfluidic device. Such an internal filter is used in addition to or instead of an external filter. An advantage of the internal filter is that it may be placed immediately adjacent to the fluid processing region, either upstream of or downstream of the fluid processing region. Placing the internal filter in such upstream locations catches unwanted particles which might pass through the external filter, if used, as well as particles which developed downstream of the external filter to the device. A challenge for the internal filter is to form many fluidically parallel filter pore passageways so that fluid can be processed with high throughput and all necessary particles caught without causing too high a fluid impedance as the filter loads up with particles.
U.S. Pat. No. 4,639,748 to Drake et al, which is incorporated herein by reference in its entirety, discloses one exemplary embodiment of a particular fabrication method for an internal filter with fluidically parallel filter pores usable in a thermal ink jet printhead. The method disclosed in the 748 patent uses a sequence of anisotropic, isotropic, and anisotropic chemical etches in a silicon wafer to form the major fluid passageways within the device, as well as to form the filter pores.